1. Field of the Invention
This invention relates to a rotary sensor and more particularly to a rotary sensor capable of detecting with high precision a rotation angle transmitted from outside.
2. Description of Related Art
A conventional rotary sensor has an approximately cylindrical housing 1 outside as shown in FIG. 6, and is provided with a case 2 having a hollow portion 2a inside, and a cover 3 securely attached on the case 2 to cover the hollow portion 2a. 
In the cover 3 a shaft hole 3a is formed. In the hollow portion 2a is housed a rotator 4 with an operating shaft 4a formed on the center of rotation. The operating shaft 4a is rotatably inserted into the shaft hole 3a of the cover 3, projecting out of the cover 3.
The shaft hole 3a is formed larger in diameter than the operating shaft 4a, so that the operating shaft 4a will be inserted loose-fit in the shaft hole 3a. 
On the center of rotation of the forward end of the operating shaft 4a there is formed, for instance, an oval engagement hole 4b, in which a later-described drive shaft 8 is inserted.
On the inside surface on the hollow portion 2a side of the cover 2, a resistor board 5 is attached. On the surface of this resistor board 5 an approximately horseshoe type resistor pattern (not depicted) is formed by printing. The resistor pattern is in contact with a wiper contact 6 attached on the rotator 4, so that the wiper contact 6 will slide on the resistor pattern with the rotation of the rotator 4, changing the value of resistance along a predetermined curve.
On the lower side of the resistor board 5 shown, a plurality of terminals 7 are attached by caulking in connection with the resistor pattern.
To detect the rotation angle of, for instance, an automotive throttle valve by the use of such a conventional rotary sensor, the cover 3 of the housing 1 is attached to a specific mounting member not shown. At this time, the drive shaft 8 (indicated by a two-dot chain line), which is connected with the rotating shaft of the throttle valve on the automobile side, is inserted into engagement with the engagement hole 4b of the operating shaft 4a. 
The forward end of the drive shaft 8 is ground into an oval form, and pressed into the oval engagement hole 4b of the operating shaft 4a to thereby transmit the rotation of the drive shaft 8 to the rotator 4.
The above described drive shaft 8 is loose or eccentric in both the thrust direction which is an axial direction and the radial direction intersecting the axial direction at right angles because of assembly requirements of components on the throttle valve side. It has become necessary to absorb this looseness or eccentricity of the drive shaft 8 on the rotary sensor side.
The looseness of the drive shaft 8 is absorbed by using the shaft hole 3a in the bottom plate 3 which is formed larger in diameter than the operating shaft 4a of the rotator 4. Thus, the rotator 4 can rotate smoothly without the operating shaft 4a interferring with the shaft hole 3a in case the drive shaft 8 is loose or eccentric in the radial direction.
The aforesaid conventional rotary sensor is of such a design that when the drive shaft 8 connected with the rotating shaft of the throttle valve rotates through a specific angle, the rotator 4 also rotates smoothly and accordingly the wiper contact 6 slides on the resistor pattern, changing the value of resistance. The amount of change of the resistance value is detected by a control section (not depicted), whereby the rotation angle of the drive shaft 8 can be detected.
The aforesaid rotary sensor, however, has the following problem: the operating shaft 4a of the rotator 4 is installed directly on the drive shaft 8 which is loose or eccentric in the thrust or radial direction; therefore with the rotation of the drive shaft 8, the rotator 4 also rotates with looseness or eccentricity in accordance with the looseness or eccentricity of the drive shaft 8. This results in deviation in the path of the wiper contact 6 relative to the resistor pattern and consequently in a failure in high-precision detection of the rotation angle.
As another method for eliminating the effect of looseness of the drive shaft 8, the drive shaft 8 and the operating shaft 4a contact on only one side in the direction of rotation to transmit the unidirectional rotation of the drive shaft 8 to the rotator 4; and with the rotation of the drive shaft 8 in another direction, the rotator 4 is driven by the force of a return spring or other mechanism, to follow the rotation of the drive shaft 8, thereby operating the drive shaft 8 and the operating shaft 4a as one body. According to this method, however, a component part such as the return spring is needed, which will increase the number of components and accordingly result in an increased cost.
It is, therefore, an object of this invention to provide a rotary sensor which can solve the above-described problems, enabling high-precision detection of the rotation angle by absorbing looseness or eccentricity of the drive shaft 8.
As the first arrangement to solve the aforementioned problems, the rotary sensor of this invention is provided with a rotator having an engagement portion with which the drive shaft is engaged, a housing rotatably supporting the rotator between top and bottom plates, and an angle sensing member for detecting the rotation angle of the rotator. The rotator has on the center of rotation an engagement portion and a shaft portion which are projectively formed on one and the other sides of the rotator; the shaft portion being supported with a support portion formed on the bottom plate and the engagement portion being so supported as to be tiltable in an arbitrary direction orthogonal to the axial direction of the support portion.
As the second arrangement to solve the aforementioned problems, a gap is formed between the top plate and the rotator, and an elastic member is inserted in this gap to support the shaft portion of the rotator in elastic contact with the support portion.
Furthermore, as the third arrangement to solve the aforementioned problems, the elastic member is made of a ring-shaped plate comprising a plurality of elastic contact portions which are partly curved in a wave form. The rotator is in elastic contact at these elastic contact portions.
Furthermore, as the fourth arrangement to solve the aforementioned problems, the rotary sensor is constituted as described below. The angle sensing member has a wiper contact and a resistor; the engagement portion stated above has a slot extending in a direction orthogonal to the axial direction of the drive shaft; and a flat plate-shaped projection is formed on the center of rotation on the forward end of the drive shaft and engaged with the slot. And the wiper contact is mounted in a position approximately orthogonal to the slot direction of the slot of the rotator.
The foregoing object and other objects will become more apparent and understandable from the following detailed description thereof, when read in connection with the accompanying drawings.